Haarlem Flights

In 1855 a slab was recovered from Germany that contained bones attributed to a pterosaur. In 1970 the slab, that had been in the Teylers Museum in Haarlem, Netherlands, was studied by John Ostrom. A short year after the description of Deinonychus was published, the portion of the animal fossilized in the slab was under the scrutiny of the meticulous paleontologist. Recognizing elements of Archaeopteryx vertebrae, ribs, and limb bones, Ostrom set about describing what then became recognized as the first discovered specimen of Archaeopteryx. Ostrom described the process in this way: 

In 1970, I was lucky to be in the right place at the right time, and with just exactly the right experience--having examined the London, Berlin and Maxberg specimens at various times during the preceding three years--and to my surprise, recognized that a fragmentary specimen displayed in a Dutch museum was not a pterosaur, as it was labeled, but actually was a fifth specimen of Archaeopteryx. The specimen consisted of two small counterpart slabs of limestone that had been found in a small quarry (now closed) north of Richstatt in 1855--six years before the discovery of the feather and the London specimen! (from Discovery, Vol. 11, no. 1, May 1975, pp. 15-23)

In describing the specimen, the paper being published in 1972, Ostrom began to become increasingly interested in the bird-dinosaur relationship. Studying the specimens of Archaeopteryx and other dinosaurs like Deinonychus, Ostrom noted that there were many similarities between birds and dinosaurs and noted specifically that Archaeopteryx "obviously represent[s] an extremely early stage in bird evolution." In the same article Ostrom recognized that his renaming of the specimen had incited not only his own interest in flight, but also that of others.

Ostrom went on to study flight origins. He specifically questioned and compared the hypotheses of tree down and ground up flight models. For those not sure of what that means, refer to this image:

©Robert Petty

Though illustrating a Chukar Partridge adult and chick in reference to wing angles for power strokes, this image conveniently shows the steps of a ground up wing movement in the left half of the image and the tree down movement in the right half of the image. Alternatively, the adult in the upper half of the image is definitely exhibiting a tree down flight from its perch while the chick is showing wing flapping from ground up as it climbs the rock. The ground up hypothesis is centered around arm and wing flapping for power and stability in an animal running up an incline whereas the tree down hypothesis centers around the idea of an animal safely reaching the forest floor from the trees. In the article linked above the hypotheses and their supporting evidence and mechanisms are well outlined by Ostrom.